1. Field of the Invention
The present invention relates to methods and apparatus for the collection, processing, and analysis of vibration data from rotating machinery.
2. Description of the Related Art
Rotating industrial machinery is present in a wide variety of environments, including petrochemical plants, power production plants, pulp and paper mills, and others. Because shutting down these machines for maintenance or as the result of component failure may involve considerable expense in lost production, preventive vibration monitoring of such machines is routinely performed. In general, vibration levels in selected frequency bands are monitored and measured on a given machine, and defects in bearings or other rolling elements may be detected before catastrophic failure occurs. With these techniques, maintenance may be efficiently scheduled. With the detection of more extreme vibration levels, the machine may be automatically shut down via relay actuation.
Vibration data processing and event detection in systems such as these was traditionally done with analog circuits, which do not lend themselves to intelligent data processing algorithms. With the advent of relatively low cost digital technology, digital signal processing and analysis has also recently been applied in these environments. In most cases, however, a large amount of analog signal conditioning and filtering is necessary. Depending on the frequency band or bands of interest, different analog filters were utilized and tuned to select desired passbands for subsequent conversion to digital data and analysis. A system of this nature is illustrated in FIG. 1. In this type of system, a host event detector 10 (which may be analog or digital in nature) is connected to a variable analog filter 12, which in turn receives an electrical signal from a transducer 14 on a machine 16 being monitored, the analog filter 12 must be rather complex and requires some type of user control 18. To be configurable for use with different machines having variable characteristic vibration frequencies. In past systems, therefore, providing a customer with tailor made vibration monitoring solutions was cumbersome and costly due to the large amount of configurable analog circuitry.
Digital signal processing techniques have been proposed to replace some or all of the traditional analog conditioning and filtering. Using a digital signal processor (DSP) to perform the required processing will hopefully allow a much more flexible system yet maintain good filter performance. U.S. Pat. No. 5,633,811 to Canada et al. describes a vibration monitoring system which uses a single fixed analog low pass filter and performs additional filtering with digital techniques. U.S. Pat. No. 5,477,730 to Carter discloses a vibration monitoring system incorporating a digital interference filter.
Although digital vibration data processing has been proposed, high quality filtering in the digital domain has not been performed accurately and efficiently. Prior art systems have also failed to address a fundamental issue in any vibration monitoring system. That is, the delay between event occurrence and event detection by the system. As the digital processing takes time, there is inevitably some delay between the moment when the analog signal appears at the input of the system, and when the processed digital representation of that signal is available for analysis. In the implementation of prior art systems such as those described in Canada or Carter above, efforts at minimizing this delay would result in further reductions in the filter quality or increases in the cost of the system to the point where its use is no longer economically feasible. There is thus a need for efficient vibration data processing and analysis methods which minimize processing time without sacrificing filter performance and without requiring excessively costly signal processing capabilities.
The present invention includes a vibration monitoring system comprising a digital filter having a time domain input coupled to an output of an analog to digital converter and a time domain output coupled to an input of event detection circuitry. The filter may have a pipeline delay of less than approximately 100 milliseconds. In advantageous embodiments, the filtering is performed in the frequency domain by a single chip digital signal processor having a maximum throughput of less than approximately 10,000,000 computations per second per channel, and wherein each channel is sampled at at least approximately 25.6 KHz.
In another embodiment, the invention comprises a vibration data processor comprising a frequency domain filter for filtering digital samples of a vibration transducer signal and a mask generator coupled to the frequency domain filter for creating and storing filter masks used by the frequency domain filter. Mask generation may be under user control. Accordingly, one embodiment further includes a user input device coupled to the mask generator for user specification of one or more frequency response characteristics of the frequency domain filter. Additional forms of user control may also be included in embodiments of the invention. Thus, the invention may include a vibration data processor comprising a pre-processor with a user selectable number of decimation stages, a user configurable frequency domain filter, and a reconstruction buffer of user selectable length. Other embodiments additionally comprise an accumulator of user selectable depth coupled between the frequency domain filter and the reconstruction buffer.